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Home Forums How can you open a file with exclusive access so no other process can read/write it? – MindStick
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1 Answers

ICSM Computer
ICSM Computer 30 May 2025
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To open a file with exclusive access in C#, you can use the FileStream constructor and explicitly set the FileShare mode to None.

Example: Open a file with exclusive access

using System;
using System.IO;

public class ExclusiveFileAccess
{
    public static FileStream OpenExclusive(string path)
    {
        return new FileStream(
            path,
            FileMode.OpenOrCreate,     // Open existing or create new
            FileAccess.ReadWrite,      // Allow reading and writing
            FileShare.None             // Do not allow any other access
        );
    }
}

FileShare.None means:

No other process or thread can open the file — not for reading, writing, or even deleting — until the stream is closed.

Usage

try
{
    using var stream = ExclusiveFileAccess.OpenExclusive("data.txt");
    using var writer = new StreamWriter(stream);
    writer.WriteLine("This file is locked for exclusive access.");
}
catch (IOException ex)
{
    Console.WriteLine("Could not access file exclusively: " + ex.Message);
}

Summary of FileShare Options

FileShare Option Allows Other Processes To...
None No access (exclusive)
Read Read only
Write Write only
ReadWrite Read and write
Delete Delete

Notes

  • Always use a using block or Dispose() to release the lock promptly.
  • On Windows, if another process tries to open the file while you have it open with FileShare.None, it will throw an IOException.
  • On Linux, file locking behavior is advisory (not enforced by the OS unless using additional mechanisms like fcntl).
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